1. Field of the Invention
The present invention relates to heat exchangers and, particularly, to such devices wherein a hot fluid and coolant are caused to flow through coaxial passages defined by double-walled tubes. More specifically, this invention is directed to improving the mechanical integrity and the efficiency of heat exchangers of the type which employ arrays of coaxial tubes and, especially, to simplifying the construction of such devices. Accordingly, the general objects of the present invention are to provide novel and improved apparatus and methods of such character.
2. Description of the Prior Art
Heat exchanger wherein a heated fluid, and particularly a pressurized hot gas, and a "coolant" are caused to flow along coaxial paths defined by the inner and outer walls of double-walled tubes are well known in the art. A heat exchanger of this type, wherein heat is transferred between two fluids separated by a tube wall, is disclosed in the publication entitled "EVT- Register No. 52/1993" at pages 40-45.
In such heat exchangers, linear arrays or tiers of double tubes extend between a pair of support structures which are known in the art as "tube plates". The tube plates are fabricated from tubular collectors, which are in fluid communication with the annular flow paths of the double tubes, and web plates through which the inner tubes of the double-walled tubes extend. Support ribs extend between the tube plates and structural elements, i.e., a support ring, which surrounds each tube plate and extends axially toward the opposite tube plate. The support rings are connected to casings which define the outer walls of plenum chambers disposed at the opposite ends of the heat exchanger. These chambers receive the fluid flowing through the inner tubes of the arrays of double tubes. The plenum chambers will, respectively, commonly function as a hot gas entry chamber and a gas exit chamber. The tubular collectors communicate with a coolant source or a coolant discharge conduit and, for this purpose, large numbers of apertures must be provided in the support rings.
Heat exchangers of the type briefly discussed above, in part because they must be able to withstand high gas pressures which act on the tube plates, need reinforcement mechanisms and thus are relatively expensive to fabricate. Additionally, coolant flow through such prior art heat exchangers, particularly between the collectors and external coolant delivery and discharge conduits, has been via a large number of relatively small diameter passages which extend through the support rings and thus has been less than optimum. Accordingly, there has been a long standing desire in the art for improvements in double tube heat exchangers.